Re: [AVR-Chat] logic levels..
2005-09-15 by Arif Deshmukh
Hi,
I also have thoughts why equipments are desinged to work in some certain voltages. Like.....
1. Most of electronic items uses 12V.
2. Radio transceiver HF/VHF/UHF work on 13.8V. (Why 13.8 such a odd figure)
Bye
Arif
On Mon, 12 Sep 2005 Anurag Chugh wrote :
>Hi people...
>Since we were talking of logic levels... i thought this would be a nice anecdote to add on..
>I wrote to one of the authors of the digital design books we use as text in college..
>on why 5v was choosen as logic one...
>this is what he has to say..
>PS please read the linked essay
>
>Anurag
>
>--------------------------------------------------------------------------------
>
>
>----- Original Message -----
> From: Anurag Chugh
>To: John F. Wakerly
>Sent: Thursday, January 06, 2005 4:49 AM
>Subject: Re: Why +5V?
>Dear Sir,
>
>I am a student of electronics engineering currently in third year of my four year course. Although I am done with Digital Design Course and should have asked this question then but it never struck me then! Just have been taking things as they were told to me. But now that I am trying my luck by constructing all sorts of circuits, (microcontroller, digital, analog et al) I find my self asking this Question : Why 5 Volts? why not any other level for logic 1.
>I tried your book but i couldnt find the answer. Maybe I didnt search well but still I suppose there is a bit of history there if there is no reason behind it.. after all if not 5Volt then what else could it be 6 or 7 ?
>It had to be something and i sure would like to know if there was any reason for it!. I used your book during the courses called Digital Design I and Digital Design II. I have never found any other author write so passionately and in so much completeness as yourself and so I thank you very much for making my DD courses real enlightening and enriching experience.
>
>Looking forward to your reply
>
>Thanking you
>
>Yours Faithfully
>Anurag Chugh
>Third Year (Electronics Engineering)
>Vivekananda Education Society's Institute of Technology (Affiliated to Mumbai University),
>Chembur, Mumbai (Bombay) - 400071
>India
>
>PS:
>Our course didnt require us to know how the gates were actually implemented, so i conveniently bunked Digital Circuits chapter when studying thoroughly for exams but I had an overview of it and I couldnt find the answer to my question there. I wonder if many other students have asked you the same question before?
>
>
>--------------------------------------------------------------------------------
>
> From: John F. Wakerly
>To: Anurag Chugh
>Sent: Thursday, January 06, 2005 4:49 AM
>Subject: Re: Why +5V?
>
>This was the voltage chosen for the original TTL family. I'm not sure of the exact reason. It's possible that some previous logic families used 5V, but then there would still be the question for that family. It was undoubtedly a tradeoff between power consumption, reliable switching operation, and noise margins.
>Or perhaps it's more like the reason that railroad tracks are separated by the width that they are (see www.naciente.com/essay94.htm).
>
>John